Plant Breeding: Definition, Steps and Types

Plant Breeding is a method used to change the genetic pattern of plant species to produce new varieties of plants that are of higher quality. These plant species are more adaptive to diseases and extreme climatic conditions such as drought, salinity, extreme temperatures, etc. They have more nutritional value and have more chances of survival in case of a pathogen/insect attack.

• Plant breeding is a branch of agricultural science.
• It deals with development of new and improved crops.
• Desired plant type can be produced by manipulating a plant species.
• The concept is as same as gene cloning (DNA cloning) of animal and microorganisms.
• It is needed to Increase the yield of crop, resistance to bugs and insects, and higher adaptability to excesses of weather and season changes. 

Key Words: Plant breeding, Plants, Crops, Resistance, Disease, Genetic species, Germplasm, Hybridization, Pollen grain

---

Steps of Plant Breeding

[Click Here for Sample Questions]

Historically, plant breeding methods involved crossing or hybridization of pure lines which further produced plants of desirable traits after artificial insemination.

There are 5 important steps to breed a new genetic species of a crop which are as follows:

Collection of variability

Genetic variability is the foundation of any breeding program

• Pre-existing variability in genes is collected from species, relatives, and wild varieties of cultivated species of crop.
• The characteristics are then evaluated and preservation for proper utilization of the natural genes is carried out.
• The entire gathering of different alleles for every gene in a crop is called Germplasm collection

​Evaluation and selection of parents 

The germplasm is evaluated for identifying the plants which have the right mix of the required characteristics.

• The chosen plant undergoes multiplication and then hybridization.
• By self-pollinating repeatedly a pure line is created when there is a requirement for the same.

Cross hybridization among the selected parents 

The parents are cross-hybridized to produce hybrid species that are a genetic combination of required characteristics in the plant.

• Cross hybridization takes a lot of time and is a difficult process as it required emasculating and bagging methods for transferring the pollen grains to the target plant.
• The success rate of the desirable characteristics showing in the hybrid has a very low probability.

Selection and testing of superior recombinants 

Plants are selected among the next generation of the hybridized generation to detect the plants with the desired mix of characters.

• The hybrid is always better than its parent species. This is called Hybrid heterosis/ vigor.
• They are self-pollinated repeatedly for many generations till a uniform and homozygous state is achieved which helps avoiding the segregation of characteristics in coming generations.

​Testing, release, and commercialization of new cultivars  

This phenomena involves following parameters.

Evaluation

The newly selected lines are carefully assessed for the agronomic quality traits, resistance to various diseases, yield, etc. by growing them in large numbers for research in open fields. 

Testing

Following the evaluation process, the line of hybrids is given to farms for testing in their fields.

• The plants are cultivated at various locations in the country with different climates and other agronomic factors for a minimum of 3 growing seasons.
• The tested crops are sent for evaluation and compared to the very best crop of the cultivar as a reference for marketing the crops. 

Release

The tested crops are then selected to be given certification and distributed wholesale to the vendors.

Also Read:

---

Green Revolution in India 

[Click Here for Sample Questions]

The Green Revolution in India helped us develop several high-yielding varieties of rice and wheat in the 1960s practicing methods of plant breeding which led to increased manifold production of foodgrain. 

Rice and Wheat

From 1960-2000, wheat production went from 11 million tonnes to a whopping 75 million tonnes and rice production went from 35 million tonnes to 89.5 million tonnes.

• The reason for this massive leap in production was the introduction of semi-dwarf varieties of rice and wheat.
• Semi-dwarf wheat was developed by Norman E. Borlaug at the International Centre for Wheat and Maize Improvement in Mexico.
• Disease-resistant and high-yielding varieties of wheat were brought in our country back in 1963 such as Sonalika and Kalyan Sona. India later developed better rice varieties like Jaya and Ratna.

Sugarcane

Saccharum barberi and Saccharum officinarum were crossed to produce better varieties of sugarcane with enhanced characteristics. 

Saccharum barberi has following characteristics.

• Grew in North India
• Poor yield
• Poor sugar content

Saccharum officinarum has following characteristics;

• Did not grow in North India
• Thick stem
• Higher sugar content

---

Plant Breeding for Disease Resistance

[Click Here for Sample Questions]

The genetic ability of a plant to prevent pathogens from causing diseases is known as Resistance. 

Plant Breeding for Disease Resistance

There are 2 Methods of Breeding for Disease Resistance:

Conventional breeding method

It is a 4 step process:

1. Germplasm is screened and selected
2. Hybrid cross of plants selected
3. Evaluation after Selection of hybrids
4. Release of new variants in the market after Testing.

Disadvantage → Disease resistant genes are less in number

Some of the variants developed through this method

Mutation breeding

A phenomenon where genetic variation is done through altering the base sequences in genes creating a new characteristic or trait which was not there in the parent generation.

• This process is done by breeding through mutations induced artificially using radiation and chemicals.
• It is a 3 step process
  • Mutations are induced
  • Selecting plants based upon resistance
  • Selected plant is multiplied and bred
• Mutations were used to introduce resistance in moong bean for the yellow mosaic virus and powdery mildew.
• Also in Abelmoschus esculentus, (Bhindi) resistance to the yellow mosaic virus was possible by the introduction of a wild species Parbani Kranti.

Read More: Genetic Diversity

---

Plant Breeding for Developing Resistance to Insect Pests

[Click Here for Sample Questions]

The plant may be immune to insect pests due to physiological, biochemical, or morphological characteristics. 

• Some of these characteristics are:
• Plants have hair on the leaves which provides resistance from jassids in cotton & from cereal leaf beetles in wheat.
• Wheat has solid stem exhibiting resistance to stem sawfly
• Cotton has smooth leaves with no nectar to resist bollworms. 
• Maize has low nitrogen and sugar but high aspartic acid to resist stem borers.

---

Things to Remember

• Plant breeding is a process to develop modified crop.
• Purpose is to manipulate plant species for more yeld, resistance against disease and high adaptation.
• types of plant breeding involves; Conventional and mutation breeding.
• Sugarcane is produced by breeding two species namely, Sacchaeirum barberi and Saccharum officinarum
• There are several more modified plants with higher yield and resistance.
• Cotton, maize, wheet etc are some examples of plant species that can give significant breeding of crop.

Also Read: